Note: Descriptions are shown in the official language in which they were submitted.
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METHODS FOR PULPING AND DEINKING
Field Of The Invention
The present invention pertains to methods for
pulping and deinking cellulosic materials such as office
waste paper.
Backqround Of The Invention
The use of recycled office waste papers as a
precursor source for paper making fibers has become
increasingly popular. Recyclable office waste paper
often contains ink and laser jet print particles. The
latter actually exist as a multiplicity of particles or
carbonized specs along the waste paper surface. The
former may be described as comprising a mixture of
pigment or organic dye, binder and solvent. Of course,
in order to recycle such office waste, the ink, including
laser print particles, must be removed in order to
provide high quality pulp stock for production of high
brightness papers.
Traditionally, deinking is accomplished with
chemical additives and a plurality of mechanical process
steps including the sequential steps of thickening the
pulp, dispersing the ink particles in the thickened pulp
in a kneading machine or the like, followed by diluting
the kneaded pulp. Then the pulp is forwarded to a
flotation cell where the dispersed ink particles are
separated via air froth flotation or the like on the
surface of the pulp slurry.
- The aforementioned deinking processes normally
contemplate usage of a repetition of the thickening,
dispersing, and flotation steps. This accordingly
presents an imposing capital expenditure especially with
regard to the thickening (i.e. washing) machines since
these are large machines, requiring excessive floor
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space, and are expensive to purchase. The same
detriments exist for the dispersing step since the
performance of these steps again requires expensive
equipment.
U.S. Patent 4,668,339 (Terry) discloses a
process for dry deinking of secondary fiber sources
wherein air dry secondary fiber batches are shredded to
produce discrete fibers and fines. The fines include ink
bearing fines or ink particles which are "dry" separated
from the fibers via vacuum/screen arrangements.
Additionally, wet deinking or cleaning steps may be
interposed between this dry shredding and the subsequent
pulping of the fibers in an aqueous slurry.
Despite the efforts of the prior art, there
remains a need for a process for deinking used office
waste paper that will minimize the need for employment of
successive thicken, disperse, flotation steps so that
capital expenditure for this equipment will accordingly
be minimized.
A more specific need exists for a deinking
process in which pulping and ink dispersion may be
achieved simultaneously by use of the same equipment so
that pre-pulping treatments such as those taugnt by the
'339 patent su~ra. may be eliminated.
SummarY Of The Invention
These and other objects are met by the present
invention. Basically, the inventive methods pertain to
the discovery that raw office waste paper of the type
imprinted with ink and laser ~et print can be
simultaneously pulped and deinked in a high solids
content, viscous aqueous mixture.
This step of simultaneous pulping and deinking
may be carried out without any upstream pretreatment
steps. Raw, untreated waste paper, such as office waste
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paper, is subjected to a kneading or shearing action in a
viscous aqueous mixture having a solids content of
greater than 20 wt.~ solids. Use of more water in the
mixture than that specified actually retards the
s mechanical kneading or shearing action of the waste paper
as it is frictionally kneaded or sheared by the machine
action and action of the high solids waste paper itself
rubbing against other waste paper.
Use of this simultaneous pulping and deinking
step has proven successful in separating the waste paper
into a homogenous mass of substantially discrete fibers
and dispersing the ink and laser printed particles
throughout this mass so that about 90~ or greater of the
ink and laser printed particles are reduced in size to
about 160 micron or less in diameter. Ink particle
reduction to such small sizes has in the past resulted in
successful ink particle separation using conventional
flotation separation and washing techniques.
After the simultaneous pulping and dispersion
step in accordance with the invention, the need for a
subsequent dispersing step is drastically reduced. This
presents tremendous savings in machine cost and floor
space requirements.
After the waste paper has been simultaneously
pulped and ink dispersed therein, the high solids viscous
mixture may be diluted to a concentration of about 2 to
5~ solids for passage through a coarse screen having
openings on the order of 0.050" to 0.125" whereby large
impurities will be maintained on the screen and
accordingly purged from the process stream.
Downstream from the coarse screen, the process
stream may be further diluted to about 0.8 to l.0~ solids
and forwarded to a centrifugal cleaner wherein high
specific gravity impurities are separated from the
pulped, process stream.
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A variety of other separatory devices may be
employed downstream from the initial centrifugal cleaning
step, ending in a final washing and thickening stage that
provides a 5 to 12~ solids deinked pulp stock ready for
bleaching and/or feed to the paper making fourdrinier or
cylinder machine.
The invention will be further described in
conjunction with the following detailed description and
appended drawing.
Brief Description Of The Drawing
Figure 1 is a schematic flow diagram
illustrating a process in accordance with the invention;
and
Figure 2 is a schematic view partly in side
elevation and partly in section of a preferred pulping
and kneading apparatus used in the process.
Detailed Descri~tion Of The Preferred Embodiments
Turning now to Fig. 1, raw, untreated office
waste paper is fed to pulping and kneading station 2.
Water is added to result in a high solids content viscous
mixture having greater than about 20 wt.~ solids,
preferably between about 20-80 wt.~ solids. At this
station, the waste paper is formed into a homogenous mass
of substantially discrete fibers and dispersed ink
particles, the latter of which are dispersed throughout
the homogenous high solids content mixture.
The type of device to be used as the
simultaneous pulping and kneading station 2 is not
critical. A variety of machines will suffice. For
example, in addition to the twin screw arrangement shown,
conventional ball mill, banbury, Hobart mixers and
Lannoye kneader-pulpers and other mixing or kneading
devices may also be mentioned.
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For the simultaneous pulping and ink (including
laser jet print particles) dispersion step, the important
- criteria are that a high solids content aqueous mixture
be mechanically subjected to compression and shearing
action. It is thought that the high solids content
requirement improves the shearing action especially and,
in contrast to the normal low solids (i.e. 5-8~) or
medium solids (8-20~) dispersion or kneading processes,
imparts a frictional force on the waste paper, thereby
improving ink particle dispersion and particle size
reduction.
Based upon presently available data, it is
desired to perform the simultaneous pulping and
dispersion step at a solids content of 20-80 wt.~. More
preferably, the solids content will be 30-70 wt.~ with
the range most preferably being 40-60 wt.~. Preliminary
data suggest that about 50~ solids is optimum.
The presently preferred apparatus for the step
of simultaneous pulping and dispersing is shown in Figure
2. This is a specially designed "Hi-Con" pulper sold by
Black Clawson Company, Middletown, Ohio. This pulper is
described in detail in U.S. Patent 4,535,943, the
disclosure of which is incorporated by reference herein.
With specific attention to Figure 2, the pulper
includes pulping tub, generally designed 110, having a
bottom wall comprising an extraction plate 112 surrounded
by tapered wall portion 113 and a generally cylindrical
side wall 114 extending upwardly therefrom.
Below the extraction plate 112 is an annular
accepts chamber 115 having a tapered bottom 116 and an
outlet pipe 117 having a conventional control valve (not
shown). An additional outlet 118 is provided for reject
material too large for passage through the extraction
plate 112.
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A rotor, generally designated 120, is mounted
centrally of the bottom wall for rotation about a
substantially vertical axis. The rotor 120 is preferably
driven by an electric motor (not shown) in a manner well-
known in the art and disclosed, for example, in Couture
U.S. Patent No. 4,109,872, disclosure of which is
incorporated herein by reference. Extending upwardly
from the rotor hub of the rotor 120 is a feed screw 130
which includes a core section 131 forming an upwardly
tapering continuation of the rotor hub. This apparatus
provides necessary compressive and shearing forces on the
high solids, viscous aqueous mixture so as to effectively
transform raw office waste or the like into a mass of
substantially discrete fibers with ink and other friable
cont~m;n~nts substantially uniformly dispersed throughout
the fibrous mass.
Another suitable apparatus for station 2 is
described in U.S. Patent 4,993,649, the disclosure of
which is incorporated herein by reference. This device
is a twin screw device in which the screws rotate in
opposite directions. Each screw shaft is tapered in its
diameter, and, in the preferred embodiment, the tapers
are disposed in opposite directions. That is, the taper
direction for one of the screws extends from left to
right (large o.d. to smaller o.d.) whereas the other
screw taper (large o.d. to smaller o.d.) extends from
right to left.
Other machines which may be used with some
modification to effect simultaneous pulping and
dispersion include those depicted in U.S. Patents
3,533,563 (Eriksson); 3,064,908 (Hjelte); 4,284,247
(Eriksson); 4,339,084 (Eriksson); 4,393,983 (Eriksson);
4,586,665 (Eriksson); 4,732,335 (Eriksson); 4,732,336
(Eriksson); and 4,655,406 (Eriksson). The disclosures of
these patents are incorporated by reference herein.
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Turning back to Figure 1, in the device 2, the
ink particles, including laser jet ink particles are
dispersed and reduced to size whereby about 90~ or
greater of the particles, after working in the device 2,
have particle diameters of about 160 microns or less.
The high solids content pulped and dispersed
ink mixture 3 is then diluted to a solids concentration
of about 2 to 3~ and forwarded to purge screen 4 located
downstream from device 2. Screen 4 has apertures that
are suitably sized to remove larger debris and waste from
the process stream so that the slurry can be pumped and
processed further.
After the process slurry is forwarded through
the purge screen, it may be diluted to a solids
consistency of about 1-1/2 to 2% and is then injected
into a liquid cyclonic cleaner 6 of the type well known
in the art in which liquids/solids separation is effected
via centrifugal action with the higher specific gravity
articles "the heavies" exiting at the bottom and the
desired, cleaned pulped slurry leaving at the top of the
device. These devices are commercially available from
The Black Clawson Company, Middletown, Ohio under the
"Ultra-Clone" trademark.
The slurry is then fed to coarse screen 8 and
fine screen 10 located downstream from liquid cyclone
cleaners 6. The coarse screen may for instance comprise
screen openings of about .050 inches to .125 inches and
the fine screen having openings of about .004 to .010
inches.
Located downstream from screen 10 is a wet
separation step, namely air froth flotation device 12.
This may for example be a IIM-BC Flotator available from
Black Clawson. This device comprises air inlet 24 which
forms bubbles in the vat to aid in floating ink and other
floatable contaminants to the surface of the liquid where
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they are separated via weir 22. The separaticn efficacy
of these machines benefits the formation of small
particle sizes and from good separation of the particles
from the paper fibers.
The slurry may then be further diluted to about
0.5~ to 1.0~ solids and fed to liquid cyclonic cleaner
stations 14,16, which may comprise, respectively,
"X-Clone" and "Ultra-Clone" cyclonic cleaners available
from Black Clawson. These, of course, provide further
cleaning, removing ink and other cont~min~nts that may
remain in the slurry.
As shown, the slurry exiting cyclone cleaning
station 16 is forwarded to washer 18 which may, for
instance, be a "D.N.T." washer available from Black
Clawson. Here the influent slurry is usually fed to the
washer at about .5~ to 1.0~ solids with the resulting
washed paper stock 20 exiting the washer beina on the
order of about 9 to 12~ solids. The washed s~ock 20 is
ready for paper forming operations or bleachirg and/or
neutralizing processes prior to paper formation.
In another embodiment (not shown) the high
solids content viscous mixture exiting station 2 may be
diluted and then fed through a coarse screen ollowed by
a fine screen. Then, it may be fed through a cyclonic
cleaner train similar to 14,16 shown in Fig. 1, followed
then by a flotation cell 12 and washer 18.
It is to be understood that in accordance with
one aspect of the invention, the office waste paper
containing secondary fibers is fed to the pulping and
dispersion station 2 without any need for pre-pulping
whatsoever (i.e. there is no pulping station Lpstream
from station 2). Additionally, it is noted that the
waste paper may be fed to station 2 in the form of bales,
without any pretreatment, or it may be sorted, shredded
or in loose form. If desirable, chemical additives,
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gases, or steam may be added before or during the step of
simultaneous pulping and dispersing at station 2.
It is apparent that the disclosed process
eliminates or drastically reduces the need for
traditional multiple thicken, disperse and float method
steps. Stated differently, after the simultaneous
pulping and dispersing step, no subsequent ink dispersion
step is needed prior to formation of the paper stock 20.
Also, save for the use of the washer 18 to form the paper
stock 20, no additional washing or thickening is
required.
While the invention has been described
primarily with regard to its use in conjunction with
office waste paper, it is noted that other recyclable
fiber sources may be included. For example, old
magazines and old newspapers may also be processed in
accordance with the invention. All of these are within
the scope of the phrase "secondary fibers" which phrase
should be construed to include all non-virgin fiber
sources.
Additionally, although the present disclosure
has emphasized the desirable attributes of simultaneously
pulping and deinking secondary fibers, the invention can
be more generally viewed as involving simultaneous
pulping and dispersion of other easily friable
contaminants. Included within the ambit of the phrase
"friable contaminants" are such items as thermoplastic
coatings, varnishes, sizes, plasticizers, as well as the
inks including xerographical and laser print inks as
referred to above. Accordingly, use of the simultaneous
pulping and dispersion step has proven successful in
transforming the waste paper into a homogenous mass of
substantially discrete fibers, separating adhering
particles from the fibers, and dispersing the friable
particles throughout the mass so that a large majority
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(i.e. about 70~ and greater, preferably 90~ or greater)
of the particles are reduced in size to about 160 microns
or less in diameter.
While there are shown and described presently
preferred embodiments of the invention, it is to be
understood that the invention is not limited thereto, but
may be otherwise variously embodied and practiced within
the scope of the following claims.
